Rate parameter indicator having meter movement smoothing at low rates

ABSTRACT

This disclosure relates to a rate parameter indicator which uniquely allows extremely accurate measuring and indicating of a rate parameter at low rates due to provision of a smooth linear signal to an indication meter circuit. The system incorporates a low-voltage drift switching circuit which is coupled to a constant reference voltage source and receptive to constant-width pulses, the frequency of which is proportional to a rate parameter. A meter jitter minimizing circuit is electrically coupled to the low-voltage drift switching circuitry, as well as the constant voltage source, and includes an averaging circuit which allows the meter jitter minimizing means to provide the aforementioned smooth linear signal to the indication meter circuit in a unique manner.

United States Patent Grundy 1 Jan. 25, 1972 [54] RATE PARAMETERINDICATOR Primary Examiner-Alfred E. Smith HAVING METER MOVEMENTAttorney-H. A. Williamson, A. G. Williamson, Jr. and J. B.

S t k SMOOTHING AT LOW RATES a [72] Inventor: Reed H. Grundy,Murrysville, Pa. [57] ABSTRACT [73] Assignee; Westinghouse Bmke Company,Swiss This disclosure relates to a rate parameter indicator which vale puniquely allows extremely accurate measuring and indicating of a rateparameter at low rates due to provision of a smooth [22] Flledi 25, 1969linear signal to an indication meter circuit. The system incor- [211App]. NO; 879 716 porates a low-voltage drift switching circuit which iscoupled I to a constant reference voltage source and receptive toconstant-width pulses, the frequency of which is proportional to a [52][1.8. CI.... ..324/l2 rate parameter. A meter jitter minimizing circuitis electrically Cl cou led to the low-voltage drift switching circuitry,as well as P [58] Field of Search ..324/l th nstant volta e source, andincludes an averaging circuit which allows the meter jitter minimizingmeans to provide the [56] References Cited aforementioned smooth linearsignal to the indication meter circuit in a unique manner. UNITED STATESPATENTS 2,681,952 6/1954 Gilbert ..324/125 x 7 4 Dmwmg F'gures 2,737,6273/1956 Lynch et al. ..324/l25 A B+ 2m f/g g Meal/2J7 Mea125? I I l f 11,5Ja I 12-4 v: m I f" *1 l l F11 I i -51w g I l Z I" 5'1 I b l l c 52, II I I vv 7 g 15 I 24 I i 2 5 I r l a. 16 22 25 I I w lk /Z0 \11 6 I l L15 m ,4, e L T J Saudis/261257 Meal/25:

Mam 17251029 Means? INVF/WIOPL :44.004 all RATE PARAMETER INDICATORHAVING METER MOVEMENT SMOOTHING AT LOW RATES My invention relates to arate parameter indicator. More specifically, my invention relates to arate parameter indicator which incorporates a meter jitter minimizingcircuit electrically coupled to an indication meter device to smoothmeter movement in the meter device during the measuring and indicatingof a rate parameter by the indication meter device at low rates. Therate parameter to be measured and indicated is represented by aproportional pulse train of constant-width pulses. The meter jitterminimizing circuit is also electrically coupled to a constant voltagereference source and is responsive to each of the above-notedconstant-width pulses. Accordingly, the meter jitter minimizing circuitgenerates over a predetermined time period, an averaging of a recurringquantity which occurs with the presence of each of the above-notedconstant-width pulses, the recurring quantity being the sum of theconstant reference voltage plus the product of a predetermined impedanceratio times the constant reference voltage, the average of the recurringquantity over a predetermined time period being the sum of the constantreference voltage plus the product of the predetermined impedance ratiotimes the constant reference voltage all times a pulse frequency factor,or duty cycle. The pulse frequency factor is defined as the ratio of thetime that a constant-width pulse is present to the time from the leadingedge of that pulse to the leading edge of the next successiveconstant-width pulse. An averaging circuit is included in the meterjitter minimizing circuit to provide the above-noted averaging of theaforementioned sums over a predetermined time period. As result, asubstantially linear indication output is provided to the indicationmeter device via the aforementioned electrical coupling between themeter jitter minimizing means and the indication meter device. Thisoutput is proportional to the rate parameter to be measured andindicated, and assures the desired meter movement smoothing in theindication meter device. This phenomenon occurs due to the fact that theproduced smooth linear indication rather than a pulsed indication isavailable for measurement at low rates.

In prior art arrangements for measuring and indicating speeds of movingobjects, there were several types of systems employed with respect tomeasuring rates of incoming pulse trains which were rate parametersproportional to object speed. One type of system included ameter-capacitor circuit whereby a capacitor was incorporated for timeaveraging of input pulses to a meter. A second type of prior artmeasuring system included a Darsonval meter which is a time averagingdevice.

Upon review of the meter-capacitor type of time-averaging arrangement,it will be appreciated that an ammeter had been placed in parallelconnection with a capacitor, the parallel arrangement receiving aconstant-width, constant-height pulse input proportional to the rate ofthe speed of an object. The capacitor charged and discharged accordingtothe presence or absence of an incoming pulse and accordingly, thevoltage characteristic of the capacitor in that environment provided anaveraging effect to be employed for provision of indications of objectspeed. This arrangement had certain undesirable features. For example,while being a fairly accurate means for indication of extremely highobject speeds, at very low speeds the capacitor voltage characteristiccurve became unsmooth and this caused the needle of the meter to waverabout the true speed of the object. Correction of this disadvantagecould only be achieved by increasing the RC time constant of themeter-capacitor circuit, since with an increased time constant measuringof low object speeds would become smooth after a permissible lag time.Since it was impossible to increase the internal resistance of the metercompensation compensation could only be achieved by increasing thecapacitance of the capacitor. Since the normal resistance of the meterwas on the order of 100 ohms, this meant that for a permissible timeconstant of 0.25 seconds the capacitance would have to be 250,000microfarads. It is obvious that such a large capacitance is highlyundesirable because of costliness,

mechanical disadvantage due to size, as well as electricalinfeasibility.

ln the above-noted second type of prior art speed measuring arrangement,the D'arsonval meter, being a very sensitive device, would tend tofollow the waveform of low speed incoming pulse trains. Readings fromthe D'arsonval meter were thus unreliable since the meter was no longertime averaging the incoming signal, but was passive in nature.

The above-noted types of disadvantages in prior art speed measuring andindication circuits being present, it is therefore desirable to employ aspeed indication system which substantially eliminates suchdisadvantages.

It is therefore an object of this invention to provide an improved rateparameter indicator with meter movement smoothing at low rates whichincorporates a meter jitter minimizing circuit which insures rateindication accuracy and readability over low rate frequency ranges.

Another object of this invention is to provide a novel rate parameterindicator which provides a smooth linear indication of the speed of amoving object by use of an operational amplifier in conjunction with afeedback averaging circuit to thereby accomplish meter movementsmoothing.

In the attainment of the foregoing objects, the present inventionincorporates a rate parameter indicator having meter movement smoothingat low rates and including in combination low-voltage switching means,constant voltage means, meter jitter minimizing means, and indicationmeans. The low drift voltage switching means is electrically coupled toa preselected reference node, and has a constant pulse-width input witha duty cycle proportional to a rate parameter. The duty cycle is definedas the ratio of the time that one constantwidth pulse is present to thetime from the leading edge of that pulse to the leading edge of the nextsuccessive pulse. The low voltage switching means is also electricallycoupled to the constant voltage means so that whenever a pulse appearson the constant pulse-width input to the low-voltage switching means, aconstant voltage remains across the low-voltage drift switching means.

The meter jitter minimizing means is electrically coupled to thelow-voltage drift switching means and to the constant voltage means.Accordingly, over the above-noted predetermined time period, the meterjitter minimizing means generates a time average of a recurring quantitywhich occurs with each constant-width pulse at the input of thelow-voltage switching means. This recurring quantity is the sum of theconstant voltage across the low voltage switching means plus the productof a predetermined impedance ratio times the constant voltage across thelow voltage switching means. The time average of the recurring quantityover the predetermined time period is the sum of the constant voltageacross the low-voltage switching means plus the product of thepredetermined impedance ratio times the constant voltage across thelow-voltage switching means all times the duty cycle of the constantpulse-width input to the low-voltage drift switching means. The meterjitter minimizing means includes averaging means which provides theabove-noted averaging of the aforementioned recurring sum over thepredetermined time period to produce a smooth linear indicationproportional to the rate parameter on an output of the meter jitterminimizing means. This output of the meter jitter minimizing means iselectrically coupled to the aforementioned indication means. Theindication means is also electrically coupled to the constant voltagemeans such that the indication means will be responsive to the linearindication on the output of the meter jitter minimizing means and willprovide an indication of the rate parameter with respect to thepredetermined reference node, i.e., the voltage level of the voltageacross the indication means will be reduced by an amount equal to theconstant voltage across the low-voltage switching means. Meter movementsmoothing is thereby assured due to the fact that the indication meansis responsive to a linear indication rather than a pulsed indication.

' minimizing means without time averaging.

FIG. lb illustrates a waveform of the output of the meter jitterminimizing means with time averaging.

FIG. 1c shows the waveform of FIG. lb as referenced to a predeterminedreference node, which is V volts above ground, where V, equals thevoltage across the low-voltage drift switching means. I

GENERAL CIRCUIT DESCRIPTION Referring now to FIG. 1 and viewing apreferred embodiment of the rate parameter indicator of the presentinvention, it will be seen that a low-voltage switching means 11 havingan input 16 is electrically coupled to a preselected reference node,which in this embodiment is ground, as well as a constant voltage means12. The low-voltage switching means includes a resistor R2 andNPN-transistor 25 having a base electrode 22, a collector electrode 23,and an emitter electrode 24. Specifically, it is seen that the baseelectrode 22 of transistor 25 is electrically coupled to the input 16 ofthe lowvoltage switching means 11; the collector electrode 23 oftransistor 25 is electrically coupled to ground; and the emitterelectrode 24 of transistor 25 is electrically coupled to resistor R2. Itshould be noted that transistor 25 is interconnected in the circuit ofFIG. 1 in a manner which is the reverse of normal transistor circuitinterconnection, namely, collector electrode 23 is coupled to ground.Reasons for such connection are set forth fully in the inventorscopending application for Letters Patent of the United States, Ser. No.879,732, filed Nov. 25, 1969, for Improved High Speed Rate Indicator,and may be simply stated that a relatively low and invariable emitter tocollector voltage, V is maintained across the transistor 25 when driveninto saturation. Hence, any electrical connection to the emitterelectrode 24 of transistor 25 is essentially and practically anelectrical connection to ground when transistor 25 is in a conductingstate.

The low-voltage switching means 11 is electrically coupled via resistorR2 to a constant voltage means 12, which constant voltage means 12includes a resistor R1 electrically coupled to a constant voltage source8+, and a diode means 20, which in the preferred embodiment of FIG. 1 isa Zener diode electrically coupled to ground. Shown in FIG. 1, is ameter jitter minimizing means 13 which includes an averaging means 10, aresistance R3, which is a meter jitter minimizing impedance means andamplifier means 30, which in the preferred embodiment of FIG. 1 is anoperational amplifier. The resistance R3 is electrically coupled to theinput side of amplifier 30 via lead 32, and the averaging means iselectrically coupled to the input and output sides of the amplifier 30via lead 32, and the averaging means 10 is electrically coupled to theinput and output sides of the amplifier 30 via leads 36 and 39,respectively. The averaging means 10 includes a resistor R4 and acapacitor C which, as shown, are in parallel connection. It is seen thatmeter jitter minimizing means 13 is electrically coupled to thelow-voltage switching means 11 via the connection of resistance R3 tonode b which is the common connection of emitter electrode 24 oftransistor and resistance R2. The meter jitter minimizing means 13 isalso electrically coupled to the constant voltage means 12 via theconnection of lead 33 from the input side of amplifier to the lead 33aat node e- As shown, an output 31 of the amplifier means 30 is electri-'cally coupled to an indication means 14 via lead 31a. The indicationmeans 14 includes an indication meter device 40 and a resistor R5 whichis an indication impedance means. The indication means 14 is alsoelectrically coupled to the meter jitter minimizing means 13 via theconnection of resistor R5 over lead 33 to the input side of amplifier30. Finally, the indication means 14 is also electrically coupled to theconstant voltage means 12 via the connection of resistor R5 over thelead 33a to the Zener diode 20.

CIRCUIT OPERATION AND FUNCTION Reference is now made to the operation ofthe rate parameter indicator of the present invention illustrated inFIG. 1. It is seen that a constant pulse-width waveform 15 is deliveredto the base electrode 22 of transistor 25 over the lead 16. Thefrequency of this constant pulse-width input is proportional to a rateparameter, the measurement of which is desirable. In the absence of thepulses on input 16 to transistor 25, the transistor 25 will, of course,be in a nonconducting state. Accordingly, there will be no voltage dropacross resistor R2, i.e., nodes 11 and b will be at the same potentialdesignated V;. In effect, the positive input terminal and the negativeinput terminal of operational amplifier 30 will be at the samepotential, and disregarding capacitor C of the averaging means 10, forthe present, amplifier 30 would produce no gain in the absence of apulse on lead 16. This is so because, as is well known, the operationalamplifier 30 will not produce a gain unless the positive terminal isdriven more positive than the negative terminal, or in this case thenegative terminal more negative than the positive terminal. Accordingly,in the absence of a pulse on input 16, and disregarding capacitor C ofaveraging circuit 10, the output 31 of amplifier 30 would be When apulse does appear at the input 16 to the base electrode 22 of transistor25, the transistor 25 will conduct, thereby producing a voltage dropacross R2 approximately equal to the voltage drop, V across the Zenerdiode 20 of constant voltage means 12, remembering that the emitter tocollector saturation voltage, V of transistor 25 is, in allpracticality, negligible. Hence, node a is essentially at a potential Vwhile node b is essentially at ground potential. Hence resistor R3 has avoltage across it relatively negative with respect to voltage V atpositive input lead 33 of amplifier 30. Furthermore, since it is awell-known fact that it is an inherent characteristic of operationalamplifiers with feedback that zero voltage exists between positive andnegative input terminals it is seen that the voltage across resistor R3is substantially V To insure that there is zero voltage between thepositive and negative input terminals of amplifier 30, the output 31 ofamplifier 30 is such that it causes the current flowing to node c, I, tobe equal to the negative of the current flowing to node b, l Since I, isitself a negative current, zero current flows toward the negative inputterminal of amplifier 30. The above-noted output of amplifier 30, in theabsence of capacitor C of averaging means 10, is accordingly equal to VrH R4/ R3)V for each pulse on input 16 to transistor 25. Hence it isnoted that in the absence of a pulse on input 16 to transistor 25 andwithout capacitor C of averaging means 10, operational amplifier 30 hasan output 31 equal to V and in the presence of a pulse on input 16 totransistor 25 and without capacitor C of averaging means 10, operationalamplifier 30 produces an output to V l'(R4/R3)V The waveform for theoutput 31 of operational amplifier 30 without capacitor C of averagingmeans 10 is shown in FIG. la. It will be noted that this waveform is apulsed waveform which if input to indication meter 40 of indicationmeans 14 would cause needle 40a to waver even though indication meter 40may have a timeaveraging capacity.

Now, with capacitor C of averaging circuit 10 being considered, thecapacitor C would begin charging toward a voltage (R4/R3)V with thepresence of each pulse on input 16 to transistor 25 and dischargingthrough resistor R4 of averaging means 10 until after a permissible timeperiod the voltage across capacitor C reaches a steady state value,thereby providing a steady state output 31 from operational amplifier 30which is equal to where i is a frequency factor or duty cycle. Thefrequency factor g is defined as the ratio of the time that oneconstantwidth pulse is present at input 16 to transistor 25 to the timefrom the leading edge of that pulse to the leading edge of the nextsuccessive pulse. The waveform of output 31 of amplifier 30, withconsideration of capacitor C of averaging means 10, is shown in FIG.IL). The time t in FIG. 12 is the point at which capacitor C is fullycharged. It will be appreciated that for the time 1,, which will varyaccording to the rate to which an incoming pulse train is proportional,meter indication will be somewhat unsmooth. But it will further beappreciated that the results achieved by the waveform of FIG. 1L) are avast improvement over the results achieved by the waveform of FIG. lg,thereby advancing the state of the art in a manner heretofore not known.It is noted that resistor R4 and capacitor C of averaging means may bechosen such that the time t, is minimal with respect to the lowest dutycycle to be measured, a feature which could not be attributed to priorart systems.

As shown, indication meter 40 of indication means 14 receives the output31 of operational amplifier means 30 via lead 31g. It will be seen thatthe indication meter 40 is also electrically connected to a potentialvoltage V at node e, through resistor R5 of indication means 14. Hence,the voltage between point f and node e, i.e., the voltage across theindication means 14 is equal to Accordingly, resistors R3, R4, and R5are chosen depending upon a desired maximum current flowing through theindication meter 40, bearing in mind that the value of resistor R4 mustconform to the value required for a minimal time constant with respectto capacitor C of averaging means 10. It will be noted that a portion ofR5 may be variable to allow adjustment if wear of the measured object ispossible, for example, wheel wear of a railway vehicle. Hence, theindication meter 40 of indication means 14 will receive a substantiallyconstant current proportional to the aforementioned rate parameter onlead 315 and meter jitter is, in practicality, nonexistant as was notthe case in prior art systems for indicating and measuring of a rateparameter at low rates.

Thus, it is apparent that the new and improved rate parameter indicatorof the present invention provides a more effective and electricallyunique method for measuring and indicating the speed of an object byproducing meter movement smoothing at lowrates.

Having thus described my invention what I claim is:

1. A meter jitter minimizing means electrically coupled to an indicationmeter device to smooth meter movement during the measuring andindicating of a rate parameter by said indication meter device at lowrates comprising, a source of constant reference voltage, a train ofconstant-width pulses, an operational amplifier means electricallycoupled to said source of said constant reference voltage and to saidtrain of constant-width pulses for producing for a predetermined timeperiod an averaging of a recurring quantity with the presence of each ofsaid constant-width pulses, said quantity being the sum of said constantreference voltage source plus the product of a predetermined impedanceratio times said constant reference voltage source, said averaging beingthe sum of said constant reference voltage source plus the product ofsaid predetermined impedance ratio times said constant reference voltagesource all times a pulse frequency factor, said pulse frequency factorbeing the ratio of the time that one of said constant-width pulses ispresent to the time from the leading edge of said one of saidconstant-width pulses to the leading edge of the next successive one ofsaid constant-width pulses, and averaging means for averaging saidrecurring quantity over a predetermined time period to thereby produce asubstantially linear indication output which is proportional to saidrate parameter and assuring said meter movement smoothing in saidindication meter device due to the fact that said linear indication isavailable for measurement rather than a pulsed indication at low rates.

2. The meter jitter minimizing means of claim 1 wherein said secondinput of said operational amplifier means is electrically coupledthrough a meter jitter minimizing impedance means to said constant-widthpulses so that said meter jitter minimizing impedance means iselectrically responsive to each of said constant-width pulses.

3. The meter jitter minimizing means of claim 2 wherein said meterjitter minimizing impedance means is a resistor.

4. The meter jitter minimizing means of claim 2 wherein said averagingmeans comprises a resistance connected in parallel combination with acapacitance, said parallel combination electrically coupled to saidoutput of said amplifier means, as well as said meter jitter minimizingimpedance means.

5. The meter jitter minimizing means of claim 1 wherein said indicationmeter is electrically coupled to an indication impedance means, saidindication meter device is electrically coupled to said output of saidoperational amplifier means and said 'uldication impedance means iselectrically coupled to said said first input of said operationalamplifier and to said constant voltage reference source.

6. The meter jitter minimizing means of claim 5 wherein said indicationimpedance means is a resistor.

7. The meter jitter minimizing means of claim 5 wherein said indicationmeter device is a Datsonval meter.

1. A meter jitter minimizing means electrically coupled to an indicationmeter device to smooth meter movement during the measuring andindicating of a rate parameter by said indication meter device at lowrates comprising, a source of constant reference voltage, a train ofconstant-width pulses, an operational amplifier means electricallycoupled to said source of said constant reference voltage and to saidtrain of constantwidth pulses for producing for a predetermined timeperiod an averaging of a recurring quantity with the presence of each ofsaid constant-width pulses, said quantity being the sum of said constantreference voltage source plus the product of a predetermined impedanceratio times said constant reference voltage source, said averaging beingthe sum of said constant reference voltage source plus the product ofsaid predetermined impedance ratio times said constant reference voltagesource all times a pulse frequency factor, said pulse frequency factorbeing the ratio of the time that one of said constant-width pulses ispresent to the time from the leading edge of said one of saidconstant-width pulses to the leading edge of the next successive one ofsaid constant-width pulses, and averaging means for averaging saidrecurring quantity over a predetermined time period to thereby produce asubstantially linear indication output which is proportional to saidrate parameter and assuring said meter movement smoothing in saidindication meter device due to the fact that said linear indication isavailable for measurement rather than a pulsed indication at low rates.2. The meter jitter minimizing means of claim 1 wherein said secondinput of said operational amplifier means is electrically coupledthrough a meter jitter minimizing impedance means to said constant-widthpulses so that said meter jitter minimizing impedance means iselectrically responsive to each of said constant-width pulses.
 3. Themeter jitter minimizing means of claim 2 wherein said meter jitterminimizing impedance means is a resistor.
 4. The meter jitter minimizingmeans of claim 2 wherein said averaging means comprises a resistanceconnected in parallel combination with a capacitance, said parallelcombination electrically coupled to said output of said amplifier means,as well as said meter jitter minimizing impedance means.
 5. The meterjitter minimizing means of claim 1 wherein said indication meter iselectrically coupled to an indication impedance means, said indicationmeter device is electrically coupled to said output of said operationalamplifier means, and said indication impedance means is electricallycoupled to said said first input of said operational amplifier and tosaid constant voltage reference sourCe.
 6. The meter jitter minimizingmeans of claim 5 wherein said indication impedance means is a resistor.7. The meter jitter minimizing means of claim 5 wherein said indicationmeter device is a D''arsonval meter.